SCHOTT Technical Glasses

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56 9.5 Passivation glasses Passivation glasses are zinc-borosilicate and lead-alumina silicate glasses used for chemical and mechanical protection of semiconductor surfaces. Processing To avoid distortion and crack formation, the different coefficients of thermal expansion of the passivation glass and the other semiconductor components must be taken into account. If the mismatch is too large, a network of cracks will originate in the glass layer during cooling or subsequent processing and destroy the hermetic protection of the semiconductor surfaces. Basically, there are three ways of overcoming this problem: The thinner the passivation glass layer, the smaller is the risk of cracking. SCHOTT therefore recommends maximum thicknesses for all homogeneous passivation layers that, as a rule, should not be exceeded. The sealing stress between glass and silicon, and thus the risk of cracking, can be reduced by slow cooling in the transformation range. As a rough rule, a cooling rate of 5 K/min is suitable for passivation layers in the temperature range T g ± 50 K. Another way of avoiding thermal expansion mismatches is using composite glasses. Composites consist of a mixture of passivation glass powder and an inert filler such as, for example, powdered ceramics with very low or negative thermal expansion. Such fillers lower the mean thermal expansion coefficient of the passivation glass and thus minimize or eliminate the risk of cracking. As a secondary effect, fillers improve the mechanical stability of the composite glass. Different processing techniques, adjusted to the requirements of the respective applications, are employed. For the manufacturing of sintered glass diodes, usually a slurry of glass powder and deionized water is applied to the diode body, including the Mo- or W-contact studs. For wafer passivation (glass applied to the Si wafer before separating the chips), an organic suspension is applied by spinning, doctor blading, sedimentation, electrophoresis, or screen printing. The organic suspension vehicles must be completely volatile or thermally decomposable below the softening temperature of the glass. Properties Electrical insulation, including dielectric breakdown resistance, generally depends on the alkali content, particularly on the Na + content. Alkali contamination in SCHOTT passivation glasses is kept low by selecting pure raw materials and special manufacturing procedures. Contamination is tested for every batch. Typical contents are below 100 ppm for Na 2 O and K 2 O, and below 20 ppm for Li 2 O. Some composite passivation glasses may contain fillers with slightly higher amounts of alkali; because the mobility of alkali ions is negligible, there is no risk of impairing the quality of the component. Polished section of a glass-encapsulated silicon diode Diodes prepared for delivery (e.g. small signal diodes)
57 Leadcontaining Type Main applications α (20/300) 10 –6 /K T g °C Pb contents wt% Firing temp. °C Holding time min. G018-205 Pb-Zn-B sinter glass diodes 4.45 541 1– 5 690 10 – – G017-388 Zn-B-Si composite thyristors, highblocking rectifiers 3.6 550 1– 5 700 5 180 ≥ 30 G017-002 Zn-B-Si composite sintered glass diodes 3.7 545 1– 5 700 10 180 – G017-096R Pb-B-Si sinter glass, planarand mesa-diodes 4.8 456 10 – 50 680 5 160 – G017-004 Pb-B-Si composite mesa diodes 4.1 440 10 – 50 740 5 160 ≥ 30 G017-230 Pb-B-Si composite transistors 4.2 440 10 – 50 700 4 160 ≥ 25 G017-725 Pb-B-Si sinter glass diodes 4.9 468 10 – 50 670 10 180 – G017-997 Pb-B-Si composite wafer passivation 4.4 485 10 – 50 760 20 180 – G018-133 Pb-B-Si composite sinter glass diodes 4.8 463 10 – 50 690 30 – – T j °C Layer thickness µm Lead-free G018-200 Zn-B-Si sinter glass diodes 4.6 557 – 665 10 – – G018-197 Zn-B-Si sinter glass diodes 4.4 557 – 675 10 – – G018-255 Bi-Zn-B varistors 9.4 396 – 520 15 – – Table 17. SCHOTT passivation glasses Heavy metals which are incompatible with semicon ductors are controlled as well. The CuO content, for example, is below 10 ppm. Because the mobility of charge carriers increases drastically with increasing temperature, a temperature limit, called junction temperature T j , is defined up to which glass-passivated components can be used in blocking operations. Forms of supply Passivation glasses are supplied as glass powders, ground iron-free and with negligible abrasion. Passivation glasses are available as tubing or sleeves for use in certain applications. They are available in various grain sizes (generally type K, see Table 17) to suit the respective application. In manufacturing, glass passivation is often followed by chemical processes (such as etching of contact windows or electrolytic deposition of contacts) which may attack the glass. The chemical resistance of the various passivation glasses differs strongly and is an important criteria in selecting the appropriate glass type. Zinc-borosilicate glasses, for instance, are highly sensitive to chemical attack by acids and alkaline solutions and therefore only recommended for use with contacts applied by sputtering. 9
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Technical Glasses Physical and Tech
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3 Foreword Apart from its applicati
Page 5 and 6: 5 7.4 PYRAN ® , PYRANOVA ® , NOVO
Page 7 and 8: 7 1 behavior, are characteristic fe
Page 9 and 10: 9 Weight loss after 3 h in mg/100 c
Page 11 and 12: 11 Surface test method B (at 121 °
Page 13 and 14: 13 Because even highly resistant ma
Page 15 and 16: 15 in the glass after 15 min of ann
Page 17 and 18: 17 a superimposed tensile stress ke
Page 19 and 20: 19 700 600 4210 Glass ΔI/I ∙ 10
Page 21 and 22: 21 lg ρ in Ω ⋅ cm --> Temperatu
Page 23 and 24: 23 Several glasses, especially glas
Page 25 and 26: 25 The transmittance τ d at perpen
Page 27 and 28: 27 Internal transmittance --> 0.99
Page 29 and 30: 29 Its thermal properties coupled w
Page 31 and 32: 31 FIOLAX ® clear, 8412 This glass
Page 33 and 34: 33 7.1 AMIRAN ® SCHOTT AMIRAN ® -
Page 35 and 36: 35 Fragmentation test for a tempere
Page 37 and 38: 37 Down-draw Molten glass Roller In
Page 39 and 40: 39 Powder Blasting shape ØB A ØC
Page 41 and 42: 41 Applications of CONTURAN ® : Pu
Page 43 and 44: 43 8 Applications of CONTURAN ® Da
Page 45 and 46: I 45 Metal (α 20/300 in 10 -6 /K)
Page 47 and 48: 47 9 Glass-to-metal sealed housings
Page 49 and 50: 49 α (20/300) [10 -6 K -1 ] Design
Page 51 and 52: 51 9.2 Glass and glass-ceramic seal
Page 53 and 54: 53 9.4 Solder glasses Solder glasse
Page 55: 55 aggressive environments (e.g. ac
Page 59 and 60: 59 crystallization in the glass, th
Page 61 and 62: 61 and unique solution, particularl
Page 63 and 64: 63 11 Optical filter glass
Page 65 and 66: 65 i-line glass ZnS FLIR Zinc Sulfi
Page 67 and 68: 67 8650 Alkali-free sealing glass f
Page 69 and 70: 69 Sealing Glasses 9 10 11 12 13 14
Page 71 and 72: 71 9 10 11 12 13 14 15 16 Heat cond
Page 73 and 74: 73 Your Contacts Advanced Optics SC
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SCHOTT Technical Glasses

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